如何使用CATextLayer为视频添加字幕

Question

我试图将字幕添加到我用应用拍摄的视频中，但我无法确定如何操作。到目前为止，我可以在一个字符串，只会增加使用此代码的整个视频：

CATextLayer *aLayer = [CATextLayer layer]; 
aLayer.frame = CGRectMake(0, 0, 320, 480); 
aLayer.bounds = CGRectMake(0, 0, 320, 480); 
aLayer.string = @"Text goes here"; 
aLayer.backgroundColor = [UIColor clearColor].CGColor; 
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:urlVideo options:nil]; 

self.cmp = [AVMutableComposition composition]; 
AVMutableCompositionTrack *trackA = [self.cmp addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; 
AVAssetTrack *sourceVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
[trackA insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:sourceVideoTrack atTime:kCMTimeZero error:nil] ; 

self.animComp = [AVMutableVideoComposition videoComposition]; 
self.animComp.renderSize = CGSizeMake(640, 480); 
self.animComp.frameDuration = CMTimeMake(1,30); 

CALayer *parentLayer = [CALayer layer]; 
CALayer *videoLayer = [CALayer layer]; 
parentLayer.frame = CGRectMake(0, 0, 640, 480); 
videoLayer.frame = CGRectMake(0, 0, 640, 480); 
[parentLayer addSublayer:videoLayer]; 
[parentLayer addSublayer:aLayer]; 

self.animComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer]; 

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; 
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [asset duration]); 
AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:trackA]; 

[layerInstruction setOpacity:1.0 atTime:kCMTimeZero]; 
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction] ; 
self.animComp.instructions = [NSArray arrayWithObject:instruction]; 
[self exportMovie:self]; 

更具体地讲，我想一些字符串添加到电影的某些帧。

Answer 1

这不是一个确切的答案，但您可以使用CAMediaTimingFunction，或者您可以使用代码中用kCMTimeZero设置字幕计时器的部分。您可以为您添加的字符串添加计时器，方法是更改​​每个要添加字幕的字符串的kCMTimer值。